1. Field of the Invention
The present invention relates to an auxiliary rotation type starter. More particularly, it relates to such a starter that when an engine for an automobile is started, a pinion is rotated before it comes to engage with a ring gear for actuating the engine.
2. Discussion of Background
FIGS. 4 and 5 show a conventional auxiliary rotation type starter. The starter is provided with a pinion 1 adapted to be engaged with or disengaged from a ring gear A which actuates an engine for an automobile. The pinion 1 is connected to an clutch inner member constituting an overrunning clutch 2. One end of a shift lever 5, which is turnable around a pivotal point, is connected to the overrunning clutch 2 and the other end of the shift lever 5 is connected to a plunger rod 4 extending from an electromagnetic switch 3 acting as an engaging switch. Engagement and disengagement of the pinion 1 with respect to the ring gear A is attained by the operation of the electromagnetic switch 3, the shift lever 5 and the overrunnig clutch 2.
The pinion 1 is rotated as follows. On turning-on of the key switch 6 of an automobile, an exciting coil 7 in the electromagnetic switch 3 is energized to attract the plunger rod 4. Then, a movable contact 8 attached to the plunger rod 4 comes to contact with two fixed contacts 9a, 9b to close a main contact, whereby a d.c. motor 10 is actuated. A torque by the armature rotary shaft of the d.c. motor 10 is transmitted to the clutch outer member of the overrunning clutch device 2 through a reduction gear device and other elements. The torque is further transmitted from the clutch outer member to the clutch inner member to thereby rotate the pinion 1.
FIG. 5 shows an electric circuit used for the starter as above-mentioned. A current is fed to the exciting coil 7 of the electromagnetic switch 3 through an auxiliary switch 11 which is also an electromagnetic switch. The key switch 6 is electrically connected between a power source (a battery) 12 of the automobile and the exciting coil of the auxiliary switch 11. The exciting coil 7 of the electromagnetic switch 3 is connected to the power source when the fixed contact of the auxiliary switch 11 is made. The exciting coil 7 is composed of a current coil 7a having a number of turn of N and a voltage coil (a holding coil) 7b having a number of turn of N. The current coil 7a is connected to the d.c. motor 10 and the voltage coil 7b is connected to the negative terminal of the power source.
When the key switch 6 of the automobile is operated, the auxiliary switch 11 is actuated, whereby a current passes in the exciting coil 7, i.e. the current coil 7a and the voltage coil 7b of the electromagnetic switch 3. Then, the plunger 4 is moved and at the same time, a current is also fed to the d.c. motor 10 through the current coil 7a to actuate the motor 10. Accordingly, the pinion 1 is rotated by the d.c. motor 10 while the plunger rod moves the overrunnig clutch 2 through the shift lever 5. In other words, the pinion 1 is rotated by the motor 10 before the pinion 1 is interlocked with the ring gear A. Under the condition, the end face of the pinion 1 slidingly touches the end face of the ring gear A and they are interlocked with each other with shift of one tooth tip. When the pinion 1 and the ring gear A becomes a sufficient interlocking condition, the movable contact 8 is brought to contact with the fixed contacts 9a, 9b, whereby the d.c. motor 10 is started under the total voltage application. Thus, the way that the pinion 1 is caused a slight rotation before interlocking with the ring gear A to obtain a desired interlocking condition is called an auxiliary rotation system.
After the pinion 1 has sufficiently interlocked with the ring gear A and the main contact has been closed by bringing the movable contact 8 of the electromagnetic switch 3 to the fixed contacts 9a, 9b, there is no substantial amount of current flowing in the current coil 7a (because of the same potential). Accordingly, the plunger 4 is held by a magnetically attracting force of the voltage coil 7b.
In the conventional auxiliary rotation type starter, the pinion 1 is brought to be in slide-contact with the end face of the ring gear A and then, is interlocked with the same when a condition of T&gt;F/g.times.r.times..mu. is established, where F is an attractive force of the electromagnetic switch 3 given when the pinion 1 is brought to contact with the end face of the ring gear A, g is a ratio in length of the shift lever, T is a torque of auxiliary rotation, r is a pitch radius of the pinion 1 and .mu. is a friction coefficient of the end faces. However, when the friction coefficient between the pinion 1 and the ring gear A is large, or a voltage is decreased, the torque of auxiliary rotation is reduced to thereby result in a condition of T&lt;F/g.times.r.times..mu., whereby the pinion 1 sometimes does not slide on the end face of the ring gear A. In this case, a sufficient amount of current can be supplied and the torque T of auxiliary rotation of the pinion 1 can be large if resistance in the current coil 7a is made small. However, on the contrary, the magnetically attracting force caused by the current coil 7a becomes large, and therefore a force for moving the overrunnig clutch 2 through the shift lever 5 also becomes large. As a result, a pushing force acting between the end faces of the pinion 1 and the ring gear A becomes large, and F/g.times.r.times..mu. also becomes large. Thus, measurements of passing a large current in the current coil 7a results in increase of the torque T as well as F/g.times.r.times..mu.. Thus, there has not been provided a fundamental resolution in the conventional starter.